Hiroki Gomi

Purely electronic terahertz polarization in dimer Mott insulators

We theoretically describe purely electronic polarization modes in terahertz frequency region in dimer Mott insulators

Photoexcited States in Dimer Mott Insulators κ-(BEDT-TTF)2X

\ensuremath{\kappa}\text{\ensuremath{-}}{(\text{BEDT-TTF})}_{2}\text{X}

STABILITY OF PHOTOINDUCED SUPERCONDUCTING STATES IN STRONGLY CORRELATED TWO-DIMENSIONAL ELECTRON SYSTEMS

. The unusual low-frequency modes arise from the coupling between the oscillation of intradimer electric dipole moments and that of alternating interdimer bond orders. These collective modes play an important role in the dynamical dielectric properties of the dimer Mott insulators. Near the phase boundary of the dimer Mott transition, the ferroelectric ground state is realized by introducing electron-lattice coupling as a result of the softening of one of these collective modes.

Auger Recombination of Photogenerated Charges in One-Dimensional Mott Insulators

We theoretically investigate the physical properties of photoexcited states in dimer Mott insulators of the form κ-(BEDT-TTF) 2 X. We adopt the quarter-filled extended Hubbard Hamiltonian on a two-dimensional anisotropic triangular lattice. The energy eigenstates responsible for the major peaks in the light absorption spectrum are numerically calculated, and their physical properties are investigated. Inter dimer charge transfer excited states form quite a broad band, and the large bandwidth mainly arises from the distribution of the kinetic energy of the photogenerated doublon and holon. The band of intra dimer photoexcited states is much narrower because of the isolated nature of the excitation. As a result, the main optical components in the lower-energy region in the light absorption spectrum are due to inter dimer charge transfer excitations, and those in the higher-energy region are due to excitations to the energy eigenstates where inter dimer charge transfer and intra dimer excited states are hybr...

Dynamics of Photoinduced Phase Transition from a Dimer Mott Insulator to a Metal

We theoretically investigate the properties of multiphoton excited states in strongly correlated two-dimensional electron systems at half-filling using the extended Hubbard model in the strong correlation case. We find that the photoinduced d-wave superconducting states are stable against the nearest neighbor Coulomb interaction within the realistic Coulomb parameters.

Multi-photon excited states of two-dimensional strongly correlated electron systems

We theoretically investigate the dynamics of photoexcited states in one-dimensional Mott insulators. We adopt the Pariser–Parr–Pople model, and numerically calculate the time development of the nonequilibrium state excited by a light pulse. In the weaker light excitation case where the maximum photoexcitation density is below about 18%, the charge carriers in the photoexcited states are holons and doublons, and the geminate recombination of bound doublon–holon pairs, namely, the Auger recombination process dominates the decay of the photogenerated holons and doublons with the realistic Coulomb parameters. In the stronger light excitation case where the density is above the value, the charge carriers of the photoexcited states cannot be described by holons and doublons. As a result, the Auger recombination process of doublon–holon pairs is not the main decay route of the photogenerated charges. Furthermore, the spin and the charge degrees of freedom are coupled, and spin relaxation occurs in the photoexcit...

Quantum Lattice Fluctuations in the Charge Density Wave State beyond the Adiabatic Approximation

We theoretically investigate the electron–phonon dynamics induced by photoexcitation in dimer Mott insulators of the form κ-(BEDT-TTF)2X [BEDT-TTF: bis(ethylenedithio)-tetrathiafulvalene, X: a counteranion]. We adopt the quarter-filled extended Hubbard Hamiltonian coupled with the dimer-bond stretching phonon modes. Utilizing the wave function where electron wave functions in the ground-state and photoexcited-state manifolds are coupled with different phonon wave functions, we solve the time-dependent Schrodinger equation numerically with a small initial disorder in the lattice. In the case where each of the dominant peaks of the interdimer charge transfer excited states is excited, the electron wave function is almost unchanged when the electron–phonon coupling constant s is smaller than the threshold value sTH. When \(s \gtrsim s_{\text{TH}}\) holds, there is an incubation time, and the decoherence of dimer-bond oscillations and the transitions to metallic states proceed simultaneously after the incubat...

Correlation Strength Crossover of Auger Recombination in One-Dimensional Mott Insulators

The effective Hamiltonian of the Hubbard model for the multi-photon excited states is derived by assuming strong Coulomb repulsion. By diagonalizing the effective Hamiltonian exactly, the lowest energy state in two-photon excited manifold is calculated in the two-dimensional Hubbard model at half-filling, and its physical properties are investigated. The antiferromagnetic spin order characteristic of the ground state is destroyed by two-photon excitation and three phases which have different electronic orders from that of the ground state are photo-generated. The analysis of several correlation functions suggests that they are of spiral spin state and two different d-wave superconducting states.

Dynamics of photoexcited states in strongly correlated electron systems.

We have developed a tractable numerical method in which large-amplitude quantum lattice fluctuations can be described beyond the adiabatic approximation using the coherent state representation of phonons. A many-body wave function is constructed by the superposition of direct products of non-orthogonal Slater determinants for electrons and coherent states of phonons. Both orbitals in all the Slater determinants and the amplitudes of all the coherent states are simultaneously optimized. We apply the method to the one-dimensional Su–Schrieffer–Heeger model with the on-site and nearest-neighbor-site Coulomb interactions. It is shown the lattice fluctuations in doped charge density wave (CDW) systems are described by the translational and vibrational motion of lattice solitons. Such lattice solitons induce bond alternation in the doped CDW system while the lattice becomes equidistant in the half-filled CDW system.

Ferroelectric states induced by dimer lattice disorder in dimer Mott insulators

We theoretically investigate the relaxation of photogenerated charge carriers in one-dimensional Mott insulators. We adopt the Pariser–Parr–Pople model, and numerically calculate the time development of the nonequilibrium state excited by a weak light pulse. We investigate the dependence of the dynamics on the Coulomb correlation strength in the case where the binding effect between photogenerated opposite charges is significant. In the strong-correlation region (\(U \gg W\)), where U is the onsite Coulomb interaction energy and W is the bandwidth, the Auger recombination where two bound holon–doublon pairs decay into one unbound holon–doublon pair dominates the decay dynamics. From the strong- to intermediate (\(U \simeq W\))-correlation regions, the Auger recombination is always dominant, but the charge carriers involved in the process cannot be described by a holon and a doublon in the intermediate-correlation region. In the crossover region between these two regions, the Auger coefficient is strongly ...